1. Field of the Invention
The present invention relates to spectroscopy, and more particularly to improvements having as a purpose the enhancing of the capabilities and the accuracy of spectroscopic analyses utilizing scattered X-rays and fluorescence that has been excited by X-rays.
2. Description of the Prior Art
The chemical composition and/or physical characteristics of materials input to industrial processes, material occurring at intermediate stages of such processes, and especially the tailings discharged, require monitoring for the purposes of process control. To be of maximum utility, the results of such monitoring need to be made available as closely as possible in time to the passage of the material through the process. Because chemical laboratory analysis of samples involves excessive delay in the availability of its results, X-ray spectroscopic analysis of such materials essentially simultaneously with their occurring in processing has been widely adopted.
Spectroscopic analysis of X-ray induced fluorescence thereof has, for example, permitted on-stream analysis, essentially in real time, of flowing slurries of metal-bearing mixtures in the course of ore processing. However, the accuracy of the results obtainable in such analyses has been adversely affected by variations in particle size of the solids, in concentration of solids in a slurry, as well as by interelement effects, and a number of efforts have been made to eliminate or minimize inaccuracies so arising.
Anderman and Kemp, in U.S. Pat. No. 2,897,367, described in 1956 a system employing means for detecting an X-ray beam at a wavelength characteristic of the analyte, or component, the concentration of which was being sought, and also detecting another X-ray beam emerging from a sample at a wavelength different from any characteristic of any component of the sample, and compensating for variations in physical characteristics, including particle size, of the sample by measuring the ratio of the intensity of the first beam to the intensity of the second beam.
Furbee and Bernstein, un U.S. Pat. No. 3,150,261, described in 1962 a system employing background radiation in compensating for variations in the solids-to-liquids ratio in a slurry.
Lucas-Tooth and Pyne in "Advances in X-Ray Analysis", 1964, 7, pages 523 et seq., described the application of computer techniques based on chemically analyzed samples of steel for correcting for interelement effects in spectroscopic X-ray analyses.
Carr-Brion and Bramwell in U.S. Pat. No. 3,749,910 described in 1970 a system using background radiation in determining the size of solid particles in a slurry.
U.S.S.R. Inventor's Certificate No. 448,374, issued to Yuri M. Gurvich et al, October 30, 1974, describes a novel method for analyzing slurries by means of X-ray spectroscopy methods, which involved making measurements of intensities of certain radiation other than the characteristic lines of the elements of interest to determine the concentrations of such elements independently of particle size. In the method described by Gurvich et al, use is made of an X-ray spectrometer, which was called a quantometer, but which is quite different from the ARL quantometer referred to hereinafter. In the method described there, measurements were made of the intensity of two lines of fluorescent radiation from the material constituting the back side of the flow cell after the radiation had traveled back through the slurry. Gurvich et al also recognized the possibility of using one or two areas of radiation scattered by the slurry at different wavelengths, including one characteristic line of the anode of an X-ray tube that supplied the exciting radiation.
The method described by Gurvich et al was intended to take advantage of the influence of total-solids concentration and particle size, on the intensity of both selected fluorescent lines of the back side of the flow cell or two areas of scattered radiation, one of which may be a source line. However, this method is far from fully effective for several reasons.
First, fluorescent lines from the back side of the flow cell can be used practically only for slurries with low absorption properties, namely, poor ores and tails of industrial processes. For rich ores or concentrates, such lines are highly attenuated by their passage through the sample in the cell and, in fact, absorbed almost completely in the first 1 to 2 mm of the cross section of the slurry's stream. Besides, the intensities of lines from the back side of the cell depends highly on geometrical conditions of measurement, including even slight variation of distance between the source of the primary X-ray beam and the flexible wall of the flow cell composed of say, capton or mylar. The intensities of such lines also depend highly on any sedimentation of solids that accumulate on the back wall of the cell. Thus, such measurements are unreliable.
Secondly, Gurvich et al disclosed for on-stream slurry analysis as a source of primary radiation, X-ray tubes with a target which supplied only one characteristic line that was scattered by the sample and detected.
Furthermore, the two wavelengths that Gurvich et al suggested be used, are both hard and are such that if they could both be detected they would fail to show any substantial difference in variation of intensity as a function of solids concentration and particle size in the slurry.
Even with the techniques disclosed in the prior art, however, it still was not possible to obtain on-stream analyses of slurries by X-ray spectroscopy comparable in accuracy to analyses obtainable by chemical analysis, especially with respect to the lighter elements. The on-stream analysis of this invention provides a much more rapid means of obtaining accurate assays of a flowing product since with it, samples can be assayed intermittently for up to 11 elements, for example, every 30 seconds with each of a large number of streams, perhaps 20 or 30, being assayed every 5 to 15 minutes in "real time".
In addition to the need for higher accuracies of assays, smelters are being penalized for excessive discharge of calcium, sulphur, or, in some cases, silicon in order to encourage the operators to reduce pollution and prolong the life of their furnaces; thus increasing the desirability of making possible on-line measurement of the lighter elements, calcium, sulphur, and silicon. Accurate measurement of sulphur concentration is also needed for general purposes and especially where copper ores are being processed.
It is a primary object of the present invention therefore, to provide a system in which, by accurately measuring these various elements on-line and compensating for physical characteristics and interelement effects, a complete assay may be obtained of the entire sample providing improved accuracy with respect to all components of interest, both components to be recovered and components to be suppressed.